x86: dynamically get/set CBM for a domain

x86: dynamically get/set CBM for a domain

For CAT, COS is maintained in hypervisor only while CBM is exposed to
user space directly to allow getting/setting domain's cache capacity.
For each specified CBM, hypervisor will either use a existed COS which
has the same CBM or allocate a new one if the same CBM is not found. If
the allocation fails because of no enough COS available then error is
returned. The getting/setting are always operated on a specified socket.
For multiple sockets system, the interface may be called several times.

Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>